#!/usr/bin/env python
"""An extended example of generators in action. Provides a function
called mergeiter that merges two iterators together.
Danny Yoo (dyoo@hkn.eecs.berkeley.edu)
"""
from __future__ import generators
def mergeiter(i1, i2, cmp=cmp):
"""Returns the "merge" of i1 and i2. i1 and i2 must be iteratable
objects, and we assume that i1 and i2 are both individually sorted.
"""
left, right = ExtendedIter(i1), ExtendedIter(i2)
while 1:
if not left.has_next():
while 1: yield ('r', right.next())
if not right.has_next():
while 1: yield ('l', left.next())
comparison = cmp(left.peek(), right.peek())
if comparison < 0:
yield ('l', left.next())
elif comparison == 0:
right.next() ; yield ('=', left.next())
else:
yield ('r', right.next())
class ExtendedIter:
"""An extended iterator that wraps around an existing iterators.
It provides extra methods:
has_next(): checks if we can still yield items.
peek(): returns the next element of our iterator, but doesn't
pass by it."""
def __init__(self, i):
self._myiter = iter(i)
self._next_element = None
self._has_next = 0
self._prime()
def has_next(self):
"""Returns true if we can call next() without raising a
StopException."""
return self._has_next
def peek(self):
"""Nonexhaustively returns the next element in our iterator."""
assert self.has_next()
return self._next_element
def next(self):
"""Returns the next element in our iterator."""
if not self._has_next:
raise StopIteration
result = self._next_element
self._prime()
return result
def _prime(self):
"""Private function to initialize the states of
self._next_element and self._has_next. We poke our
self._myiter to see if it's still alive and kicking."""
try:
self._next_element = self._myiter.next()
self._has_next = 1
except StopIteration:
self.next_element = None
self._has_next = 0
def _test():
for item in mergeiter([2, 4, 6, 8], [1, 3, 4, 7, 9, 10]):
print item
if __name__ == '__main__':
## _test()
import sys
f1, f2 = open(sys.argv[1]), open(sys.argv[2])
for item in mergeiter(f1, f2):
print item
